In a general vehicle air conditioner, a vapor-compression type refrigerant cycle device is adopted as a temperature adjusting portion. The temperature adjusting portion adjusts a temperature of air blown into a vehicle compartment that is an air-conditioning target space. Moreover, in order to reduce the environmental impact such as global warming, refrigerant having a low global warming potential is required to be adopted as refrigerant of the refrigerant cycle device.
Patent Documents 1 and 2 (JP 2010-101553A corresponding to US 2011/0192187A1, and JP 2010-255906A) propose a refrigerant cycle device, in which a relatively new refrigerant such as R1234yf is adopted as refrigerant of the refrigerant cycle device. The relatively new refrigerant has a low global warming potential relative to conventional refrigerant, such as R404a, R410a or R134a, that has been used generally.
Even if the relatively new refrigerant is adopted as refrigerant of an existing refrigerant cycle device used generally for the conventional refrigerant, and if the existing refrigerant cycle device is operated in a conventional operation state, it may be difficult to provide a temperature adjusting performance equivalent to that of a case, in which the conventional refrigerant is adopted as the refrigerant of the existing refrigerant cycle device, in the conventional operation state.
As shown in FIG. 11, R1234yf, which is an example of the relatively new refrigerant, is higher by approximately 20% in density than R134a that is an example of the conventional refrigerant. Thus, when R1234yf is adopted as refrigerant of an existing refrigerant cycle device used generally for R134a, a refrigerant circulation rate in the existing refrigerant cycle device is required to be increased by approximately 20% in order to provide a temperature adjusting performance equivalent to that in a case in which R134a is adopted as the refrigerant of the existing refrigerant device.
The increase of the refrigerant circulation rate causes an increase of a level of a refrigerant passing noise which is generated when refrigerant passes through a cycle components of the refrigerant cycle device. When the existing refrigerant cycle device, in which the relatively new refrigerant is adopted, provides the temperature adjusting performance equivalent to that of the existing refrigerant cycle device, in which the conventional refrigerant is adopted, it may be difficult to keep a sound level of the refrigerant passing noise generated in the existing refrigerant cycle device in which the conventional refrigerant is adopted.
For example, when an air-conditioning thermal load determined based on a condition of the air-conditioning target space is high at an activation time of the compressor for the refrigerant cycle device, the compressor discharges a large amount of refrigerant. Hence, the refrigerant passing noise may become harsh to a passenger. Furthermore, such increase of the refrigerant passing noise may occur not only in a case of R1234yf but also in a case of refrigerant having a higher density than the conventional refrigerant.